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Temperature (Air/Water/Snow):
Air temperature is
the ambient temperature of the air and water vapor as
measured by a thermometer or other measuring device
in which the thermal element is dry and shielded from
radiation. Water and snow temperature are measured with
a measuring device in direct contact with the environment.
Available units are Fahrenheit – a temperature scale where
water at sea level has a freezing point of +32° F°, and a
boiling point of +212° F; and Celsius – a temperature scale
where water at sea level has a freezing point of 0° C and a
boiling point of +100° C.
Relative Humidity:
The ratio of the amount of water
vapor in the air at a specific temperature to the maximum
amount that the air could hold at that temperature,
expressed as a percentage. Relative humidity is a function
of temperature and therefore changes as the temperature
changes, even if the amount of moisture in the air remains
constant.
Heat Stress Index:
A measurement of the air
temperature in relation to the relative humidity, used as
an indicator of the perceived temperature.
Dew Point:
The temperature at which the water vapor in
the atmosphere begins to condense. Any further cooling
causes condensation (fog and dew). This is also the
temperature of saturation at which the dry-bulb, wet-bulb
and dew-point temperatures are all the same.
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Wet Bulb:
The lowest temperature in the ambient
atmosphere yielded by evaporating water from a wet
muslin-covered bulb of a thermometer.
Glossary of Measurements
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Absolute/Station Pressure:
The actual measured pressure
of the weight of air above the measurement point. Often
called station pressure.
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Density Altitude:
The equivalent altitude in the ICAO
standard reference atmosphere for the measured temperature,
relative humidity and air pressure. A measure used primarily by
pilots, high-performance engine mechanics and long-range
shooters.
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